Normals and light

Why a face turned toward the sun is brighter than one turned sideways, and how one formula computes it. Then how a rock of a couple of thousand triangles can look as if it has a million.

Why this matters

Light is what makes a 3D picture look solid. Without it, a model is a flat silhouette filled with color. The engine works out the lighting for every pixel, and almost all of that calculation rests on one quantity: the normal.

Once you see how a normal becomes brightness, a lot falls into place. You know why normal maps exist and why models sometimes look faceted or puffy. You know why bumps sometimes turn into dents after an import, and how moss knows which side of a rock is the top.

Further in the article

1. The normal
2. Why the face toward the sun is brighter
3. The normal map
4. Why the map is lilac
5. Spotting the fake
6. Where the map comes from
7. Where it breaks
8. Connections: the same idea in other fields
9. Key points
10. Test yourself